The present invention relates to a jig designed for retaining the mitered corners of window and door frames fashioned from molded plastic section, in fixed position during welding, and for releasing same thereafter.
Conventionally, the sash and surround frames of plastic window and door fixtures are formed by effecting a fluch miter between the ends of each two abutting members, which are previously cut to size and shaped to the necessary 45.degree. angle at either end, and welding the abutting surfaces together.
The prior art embraces jigs with special clamp assemblies, mounted on sliding carriages, that can be transversed during operation into positions corresponding to the four corners of the frame. Each such clamp assembly affords a substantially square surface by which the mitered ends of the two relative members of the frame are supported; the surface is embodied in two distinct parts that appear as a pair of horizontal triangular rests, associating by way of their hypotenuses in such a way that the joint between them coincides substantially with the 45.degree. angle of the weld line between the mitered ends of the two frame members. Each of the single triangular rests (of which there are eight, clearly enough) is integral with a respective fence designed to check the relative member laterally and ensure its correct position in the horizontal plane. More exactly, of the eight fences, four are positioned transversely, engaging the rails of the frame; the remaining four engage the uprights, and lie parallel to the path along which the frame exits from the jig.
Finally, each clamp assembly comprises pairs of plates, positioned above the rests, that serve to hold fast the members (uprights and rails) when being positioned, and during the subsequent welding step.
Work is fed manually to jigs of this prior art type by an operator, standing alongside, who first positions one rail, then the two uprights, and finally, the remaining rail. The most convenient procedure is to position the two clamp assemblies farthest from the operator initially within reach, so that the first rail can be introduced without difficulty, before traversing them away through a distance that will accommodate the length of the uprights; the uprights are then positioned, and the frame completed by adding the second rail.
Having proved successful as far as regards the faultless fabrication of frames for molded plastic fixtures, these conventional jigs nonetheless are beset by certain serious drawbacks.
A first drawback is that the operator experiences no small difficulty in positioning the longitudinally disposed, upright members of the frame, inasmuch as the clamp fences are fixed, and the four transverse fences therefore constitute a permanent obstacle placed across the jig. Accordingly, to negotiate these four transverse fences and insert the upright members of the frame between them, parallel with the longitudinal axis of the jig along which the welded frame is removed, the operator has to grasp the moldings by one end, cantilever them forward, and force them into place.
This method of proceeding gives rise to an inherent handling difficulty, affecting the operator. Since the operator must effect the positioning operation repeatly during continuous production, an individual will be subjected to increasing physical strain of an order commensurate with the length of the frame uprights being handled.
A second drawback, likewise stemming from the fact that the transverse fences are fixed, is that a conventional jig can not be set up for automatic feed through a horizontal path tangential to the plane occupied by the frames, precisely because of the obstruction caused by the fences.
Accordingly, the object of the invention is to eliminate the aforementioned drawbacks.